Electrical exposure time control device for use in a photographic camera

ABSTRACT

A camera includes a shutter whose closing is actuated by an electromagnet controlled by an electrical timing circuit which is provided with a photosensitive element and a circuit disabling switch. A pair of accessible coupling terminals are connected to the opposite ends of the electromagnet. An accessory is separably mounted on the camera and includes a photosensitive element controlled timing network having an output provided with a pair of coupling terminals which separably engage the electromagnet terminals and the disabling switch may be manually opened or is opened automatically with the coupling of the terminals. More than one shutter control accessory may be provided and the timing circuits may be of different types, with different fields of light responsiveness and with manually selectively adjustable timing intervals.

United States Patent Hayashi et al.

[ ELECTRICAL EXPOSURE TIME CONTROL DEVICE FOR USE IN A PHOTOGRAPHIC CAMERA [75] Inventors: Toshio Hayashi; Akira Yoshizaki;

Japan Minolta Camera Kabushiki Kaisha, Osaka-fu, Japan Filed: Aug. 2, 1973 Appl. No.: 385,004

Assignee:

Foreign Application Priority Data Aug. 7, i972 Japan 47'783ll References Cited UNITED STATES PATENTS 8/1971 Langnan 95/10 C 5/1973 Kotano Yata 95/10 CT Kayoshi Tsujimoto, all of Osaka-fu, 7

in] I 3,812,499

1451 May 21, 1974 Primary ExaminerJoseph F. Peters, Jr. Attorney, Agent, or Firm-Wolder & Gross [5 7 ABSTRACT A camera includes a shutter whose closing is actuated by an electromagnet controlled by an electrical timing circuit which is provided with a photosensitive element and a circuit disabling switch. A pair of accessible coupling terminals are connected to the opposite ends of the electromagnet. An accessory is separably mounted on the camera and includes a photosensitive element controlled timing network having an output provided with a pair of coupling terminals which separably engage the electromagnet terminals and the disabling switch may be manually opened or is opened automatically with the coupling of the terminals, More than one shutter control accessory may be provided and the timing circuits may be of different types, with different fields of light responsiveness and with manually selectively adjustable timing intervals 12 Claims, 7 Drawing Figures owltchlnq circuit SHEEI 1 0F 5 switching circuit FIG! PATENTEDMAY 21 mm i l l switching circuit PATENTED m 21 m4 SHEET 3 BF 5 light measuring PATENTEDHAYZI 1974 I 38121499 SHEET u UF 5 PATENTEDMAY 1 IBM :3 a 1 2.499

SHEET 5 OF 5 switching circuit switching circuit i i H timing circuit i i siorcige meter circuit Circuit i i l i light measuring :P circuit ELECTRICAL EXPOSURE TIME CONTROL DEVICE FOR USE IN A PHOTOGRAPHIC CAMERA BACKGROUND OF THE INVENTION The present invention relates generally to an improved electrical exposure time control device for use in a photographic camera provided with a shutter of the type in which the completion of the exposure is effected through the actuation of an electromagnet, and more particularly to an electrical exposure time control device for use in a photographic camera, comprising a camera body provided with at least an electromagnet and the accessible terminals connected to the opposite ends of the electromagnet solenoid and an accessory which can be mounted on the camera body, the accessory having on its output side an electrical control circuit for the generation of a voltage; whereby the output from the accessory electrical control circuit may actuate the electromagnet within said camera body for com trolling the exposure, with the output terminals of the electrical control circuit being coupled to the terminals which are connected across the electromagnet solenoid.

An electrical exposure control device is well known, in which the output from an electric control circuit actuates an electromagnet so as to control a shutter. In such a known device, an electric control circuit and an electromagnet areincorporated in the camera.

There have been many proposed mechanisms for controlling the exposure for a camera. For instance, in the case of an automatic control of shutter speed, including that employing a light receiving element, there are types which control the diaphragm opening and shutter speed simultaneously, which control the shutter speed with a diaphragm being preset, or which control the diaphragm with shutter speed being preset. Furthermore, in the case of an automatic exposure control, there are known a control device using the scene light which has been transmitted through an objective lens, a control device which uses the scene light which has not been transmitted through an objective lens, a control device which spot-measures the light from a specific object in a scene, etc. In the case of a single lens reflex camera, when an attempt is made to control the exposure by using a scene light which has been transmitted through an objective lens, many circuits are required, such as, a light measuring circuit which produces an output voltage corresponding to the logarithm of the luminance of a scene, a storage circuit which stores an output voltage from the light measuring circuit, a timing circuit which provides a time delay by means of an electric current which has been antilogarithm converted from the stored voltage in the storage circuit, a switching circuit adapted to be operated by means of an output from the timing circuit, an electromagnet which is operated by means of an output from the switching circuit, a constant current circuit, a compensating circuit which compensates for a temperature variation, and a circuit which operates from the output from the light measuring circuit by setting photographing conditions such as diaphragm value and film sensitivity. Such circuits themselves are quite complex, and, in addition, there are required many other circuits such as those which switches a circuit for controlling the exposure by setting the aforesaid exposure time manually and a circuit for use in spot-light measurement. Ac-

cordingly, even if as many of the elements as possible are in integrated circuits, it would be impossible to incorporate so many elements in a compact size camera.

As a result, in the conventional camera, an automatic exposure time control system is of limited application, i.e., it would be impossible to incorporate all kinds of automatic exposure time control systems therein.

OBJECTS OF THE INVENTION The present invention is directed to avoiding such disadvantages which have been experienced with camerasof the prior art.

Accordingly, it is an object of the present invention to provide an electrical exposure time control device for use in a photographic camera which enables various types of exposure time controls, without increasing the bulk of a camera body.

It is another object of the invention to provide an electrical exposure time control accessory device for use in a photographic camera which can control the shutter exposure time by actuating an electromagnet housed in the camera by using the output from an exposure time control circuit, the accessory being mountable on the camera body incorporating an exposure time control circuit, so as to be electrically connected across said electromagnet through output terminals of the exposure time control circuit in said accessory.

It is a further object of the invention to provide an exposure time control circuit for use in a photographic camera, in which an electromagnet adapted to control the completion of the exposure interval by means of the shutter is incorporated in the camera body, and another exposure time control circuit is incorporated in a camera accessory which is mountable on the camera body, whereby, by mounting the accessory on the camera, the output terminal of the accessory exposure time control circuit is connected across the electromagnet inside the camera and thus the output from the accessory exposure time control circuit may control the aforesaid electromagnet so as to control the shutter exposure.

It is a still further object of the invention to provide an electrical exposure time control device for use in a photographic camera, in which an electromagnet is incorporated inside a camera body for controlling the completion of the exposure interval by means of a shutter, exposure time controlcircuits of different types are incorporated in a plurality of accessories selectively mountable on the camera, and the output terminals of the accessory exposure time control circuits are selectively connected across the aforesaid electromagnet, whereby the exposure time control circuits thus connected actuate the aforesaid electromagnet so as to control the exposure time of the shutter.

SUMMARY OF THE INVENTION The objects of the present invention attained in an electrical exposure time control device for use in a photographic camera, comprising a camera body which is provided with an electromagnet which controls the completion of the exposure by means of the shutter, an

accessory being provided which is adapted to be mounted on the camera body, the accessory incorporating at least one exposure time control circuit. With this arrangement, the aforesaid accessory is mounted on the camerabody and the output terminals of the exmovable between the viewing position and the picture taking position or may be of the type which lacks a movable reflector.

The electromagnet incorporated in the camera body may be of the type in which the completion of the exposure by means of a shutter is controlled when the electric current, which has been interrupted, begins to be fed or when the electric current, which is being fed, is interrupted, and furthermore, the shutter may be of the between-the-lens or focal plane type.

Any type of accessory structure may be used for mounting on the camera body, as far as it may be mounted for the photographing purpose, for instance, it may be a housing used for a pentagonal prism or may be an accessory used only for the purpose of housing an exposure control circuit for a special exposure time controlling purpose.

The exposure time control circuit as used'in the present invention may be a circuit which controls the exposure time set manually or may be a circuit which contains a light receiving element and in which the light receiving element automatically controls the exposure time in response to the electric current produced in response to the incident light, or both. Furthermore, the aforesaid light receiving element may receive the light which has been transmitted through an'objective lens or the light which has not been transmitted through an objective lens from the scene. In the former case, the light receiving element may receive the scene light attenuated by a diaphragm which has been adjusted with the camera diaphragm aperture at the time of photographing or it may receive the scene light which has been transmitted through an open diaphragm and then the exposure time control circuit operates for the exposure time, commensurate to the diaphragm value adjusted at the time of photographing, to thereby produce a control output, or it may be of the type in which a light receiving element receives the light from the entire scene, or may be of the type in which a light receiving element receives the light froma specific object in the scene.

Furthermore, the camera body may be such as contains either one of the aforesaid various types'of exposure time control circuits, in addition to the electromagnet. In this case, the connection of the output terminal of the exposure time control circuit with the electromagnet may be interrupted by means of the connection across the electromagnet within the camera body,

I of the output terminals of an exposure time control circuit contained in the accessory.

BRIEF DESCRIPTION OF THE DRAWINGS a pentagonal prism container as shown in the embodiment of FIG. 1;

FIG. 3 is a longitudinal cross sectional view of the connecting terminals of the camera body and accessory shown in FIG. 1;

FIG. 4 is a circuit diagram of another embodiment of the present invention;

FIG. 5 is a perspective view, partly broken away of a part of a camera body and an accessory consisting of a pentagonal prism;

FIG. 6 is a longitudinal cross sectional view showing a connecting terminal of a camera body accessory and a switch shown in FIG. 5; and

FIG. 7 is a circuit diagram of a still further embodiment of the'present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and particularly FIGS. 1 to 3 thereof which illustrate a first embodiment of the invention, in which there are incorporated in a camera body an exposure time control circuit G as shown in FIG. 1 and an electromagnet M which is adapted to be energized or actuated by the output from the circuit G, the electromagnet being adapted to be actuated also by an exposure time control circuit H which is incorporated in an accessory B adapted to be mounted on a camera body A.

The exposure time control circuit G includes a light receiving photosensitive element P which receives the light from the entire scene. The light receiving element P and a variable resistor R which serves to manually set the exposure time, are connected at one end and their other ends are connected to respective contacts of a switch S whose arm is connected to a capacitor C,,, and a normally closed trigger switch S is connected across the capacitor C, and is opened upon the commencement of the shutter exposure, thus constituting a timing circuit energized by an electric power source B, through a switch S The junction point of the photoelement P or resistor R, with the capacitor C is connected to the input of a switching circuit F Connected to the output terminal of switching circuit F,, is an electromagnet M, that is, the solenoid thereof, with the both ends M and M, thereof being connected through the lead lines 1 Aand IE to a dual terminal coupling 3A.

On the other hand, in the exposure time control circuit I-l incorporated in the accessory or housing B, a light receiving photosensitive element P,,, which is adapted to receive only the light from an object located at a specific location in a scene, and a variable resistor R,,, which is adapted to manually set the exposure time and which is connected to said light receiving element P are both connected to respective contacts of a switch S whose arm is connected to a capacitor C and a normally closed trigger switch S is connected across the capacitor C trigger switch S being adapted to be opened upon the commencement of the shutter exposure, thus constituting a timing circuit together with an electric power source E The junction point of photoelement P or resistor R to the capacitor C is connected to the switching circuit F with the output terminal being connected to a lead line 18,

while a lead line 2,, is connected to the other pole (negative pole) OF electric power source E with the other terminals of the both lead lines 18 and 2B being connected to respective terminals of a coupling 38.

In FIG. 2 there is shown the camera body A and an accessory B, i.e., a single lens reflex camera body A and a housing B of a pentagonal prism which is removably mounted on the camera as an accessory in registry with a focussing screen 8 of the camera body A.

The camera body A is provided with the aforesaid electrical connector or coupling 3A on its casing wall and also includes a known film winding shaft 5, a film winding lever 4 and a film rewinding shaft 6. The camera body further houses the exposure time control circuit G, i.e., an integrated circuit K consisting of the related electric elements and an electromagnet M connected to the output terminal of said circuit, whereby the actuation of energization of the electromagnet M will operate to release the rear curtain of a curtain shutter (not shown) in a known manner. Shown at 7 is an exposure time setting dial adapted to be manipulated manually at 8 the aforesaid focussing screen, at 9 a latch member adapted to releasably lock the pentagonal prism housing in registry with the focussing screen.

mounted on the camera body A. Designated at 11 is a film sensitivity setting dial and at 13 an eyepiece of a finder. The exposure time control circuit H within the housing B is an integrated circuit L, in which as many components are integral-circuited as possible, and there is provided a meter 12 adapted to be operated by the output from the exposure time control circuit H. A pair of leads 1B and 2B, which are connected to the circuit output terminal and one pole of the electric power source E run through a small hole 14 in the housing wall to the outside of the housing B, with the ends thereof being connected to the terminals of coupling 3B.

The coupling 3A, as shown in FIG. 3, includes a conductor tube 16 having flange l5 and is fitted in an opening in the casing of the camera body, the tube having a guide slot 16a extending axially thereof. An insulating sleeve or tube 18 which has a projection 18a engaging a guide slot 160 in tube 16 vertically slideably engages conductor tube 16. A conductor tube 22 of small diameter is anchored by an insulating member 21 to a bottom end wall 17 of the conductor tube 16, while the insulating tube 18 engages the outer face of conductor tube 22.

The lead wire 2A connected to one terminal M, of the electromagnet M is connected to the conductor 16 for grounding, while the lead line 1A connected to the opposite terminal of the electromagnet M is connected to the conductor tube 22 insulated from the conductor tube 16.

A movable resilient contact piece or arm 20 of a switch 8,, which is engagable within the guide slot 16a with the projection 18a of the insulating tube 18, is normally resiliently urged against a fixed contact 19 to thereby normally close the switch S and maintain the insulating tube 18 in its uppermost position.

The coupling 38 is provided with an electrically conductive cap 23 adapted to be fitted on the flange 15; an insulating plate 2 having a depending tubular projection 24a which is adapted to depress the insulating tube 18 against the elasticity of the movable contact piece 20, while engaging the upper face of the insulating tube 18 when the cap 23 is fitted on the flange 15. A conductor pin 25 engagable with the bore 21 in the conductor tube 22 is coaxially anchored to the cap 23,

while the lead line 18 is connected to the pin 25 and the lead line 28 is connected to the cap 23, respectively.

Accordingly, when the connecting terminal 3B is not fitted in the connecting terminal 3A, theswitch will be in a closed position and thus the exposure time control circuit G will be in an operable condition. On the other hand, when the couplings 3A and 3B are brought into engagement with each other, the switch S is opened and as a result the exposure time control circuit G is in a disabled or rest condition. In addition, the output terminals of a switching circuit F of the exposure time control circuit H are connected by lead lines 1B and 28 to the respective terminals of the electromagnet M, whereby the exposure time control circuit H actuates and controls the electromagnet M, while the exposure time is controlled in response to the brightness of the incident light from a specific object in the scene or field, said light being received by the light receiving photosensitive element P According to another embodiment of the present invention as shown in FIGS. 4 to 6, there are provided, within the camera body, an exposure time control circuit G, the same as that in the first embodiment, and an electromagnet M operable by the output therefrom. An exposure time control circuit H within the pentagonal prism housing B, such as shown in the firt embodiment, measures the brightness of the scene light which has been transmitted through an objective lens and thereby controls the exposure time based on the measurement thus obtained. More specifically, the exposure time control H is provided with a light measuring circuit, a metering circuit 0 indicating the output voltage from the light measuring circuit, a storage or memory circuit N for storing the output voltage from the light measuring circuit, a timing circuit U adapted to produce an output commensurate with the voltage stored in the storage circuit N, and a switching circuit F operated by the output from the timing circuit U, whereby the switching circuit F produces an output for use in controlling the exposure time.

An accessory D, other than the aforesaid pentagonal prism housing B, may be mounted on the camera body A, while the exposure time control circuit J incorporated in the accessory D is the exposure time control circuit having a light receiving photosensitive element P adapted to exclusively receive the light from an object located at a specific position in a field of view or scene, as in the case with the exposure time control circuit H in the first embodiment.

As shown in FIG. 5, there is provided an opening 33 in a circumferential wall around the focussing screen of the camera body A, through which opening there is provided access to contact pieces 1A and 2A, with the contact piece 1A being connected to the terminal S of a switch S and being further adapted to be connected through the movable contact piece of switch arm S and lead line 1A, to terminal M of the electromagnet M. Connected to the terminals of coupling 3A are one terminal M of the electromagnet M and the other fixed contact S of the switch 8:.

Furthermore, there are provided contact pieces 1B and 28 connected through lead lines 18 and 23 to the output terminal of the exposure time control circuit H outside the pentagonal prism. Thus, when the container B is properly mounted to the focussing screen 8 of the camera body A, the aforesaid contact pieces 1A and 18 will be broughtinto contact with each other, and

so will be the contact pieces 2A and 2B.

The lead lines 1D and 2D, which are connected to the output terminals of the exposure time control circuit incorporated in the accessory D, are connected to respective terminals of coupling 3D.

As shown in FIG. 6, the connecting terminals 3A and 3D are substantially the same as those in the first embodiment and accordingly the description will be omitted except for their differences.

The conductor tube 16 of the'coupling 3A attached to the casing wall of a camera body A is formed with two guide slots 16a and 16b, while an insulating tube 18 registering with the conductor tube 16 is formed with two projections 18a and 18b which fit in the guide slots 16a and 16b.

A switch lever 30, one end 30c of which engages the underside of the projection 18a within the guide slot 16a, is swingably journalled in the camera body A, being biased to urge the insulating tube 18 upwards under the influence of a spring 32, while the other end of the switch lever 30 engages the movable contact piece or arm of the switch S,, the movable contact piece 20 being resiliently self-biased against the fixed contact piece 19 so as to close the switch S and thus the exposure time control circuit G normally actuates the electromagnet M. An arm 30b extends through and projects beyond an opening 31 provided in the top face of the casing of the camera body A in a position above the'switch lever 30. Accordingly, when the housing B is properly mounted on the camera body A, the arm 30b is urged downwards by the housing B, and the switch lever 30 is rotated against the action of the spring 32 in a counterclockwise direction to thereby open the switch 8, against the bias thereof. At this time,

.the contact piece 1A is brought into contact with the contact piece 1B and the contact piece 2A into contact with the contact piece 2B.

In this respect, although the insulating tube 18 tends to be depressed by gravity relative to the conductor tube 16, the insulating tube 18 is maintained in a position as shown in FIG. 6, because the arm or movable contact S of the switch S engages the underside of the projection 18b, with the free end of movable contact piece S being urged upwards by its resiliency within the guide slot, and the contact piece S tends to contact the contact piece S such that the projection 18b is arrested against being urged downwards. At this time, the switch S allows the output from the exposure time control circuit H to be connected to the electromagnet M.

On the other hand, when the coupling 3D is connected to the coupling 3A in the manner as in the first embodiment, a depending projecting collar 240 on the coupling 3D urges the insulating tube 18 downwards to cause a conductor pin to engage the bore 21 in a conductor tube 22 of reduced diameter, while causing the movable contact piece S to be lowered so as to contact the contact piece S Accordingly as shown in FIG. 4, the connection of theexposure time control circuit H with the electromagnet M is interrupted, such that the output of the exposure time control circuit within the accessory B will be connected via the lead lines 1D and 2D to the terminals M, and M, of the electromagnet M.

Thus, when the housing B is not mounted and the coupling 3D is not connected to the coupling 3A on the camera body, the electromagnet M will be actuated in response to the brightness of theentire scene, by means of the output from the exposure time control circuit within the camera body A. On the other hand, when the housing B is mounted in the camera body A, then the electromagnet M will be actuated by the exposure time control circuit H in response to the brightness of the light which has been transmitted through the camera objective lens. Furthermore, when couplings 3A and 3D are interconnected, the electromagnet M will be actuated by the exposure time control circuit J incorporated in accessory D in response to the brightness of the light from an object located in a limited specific position in the scene. Thus, it will be recognized that the exposure time may be controlled according to various controlling methods or conditions.

A still further embodiment of the present invention is shown in FlG. 7. In the second embodiment described above the switches S, and S are designed to be automatically switched with the housing B being mounted on the camera body A as well as with the both couplings 3A and 3D being interconnected. In contrast thereto, according to the embodiment shown in FIG. 7, there is provided a switch S separated from the couplings described above, such that the exposure time control circuits G, H, J may be selectively used by manually actuating the switch S More particularly, the electromagnet M may be actuated by means of the exposure time control circuit G within the camera body A, with the movable contact piece or arms of the switch 8;, being connected to the terminal S the electromagnet M may also be actuated by the exposure time control circuit H with the movable contact piece S engaging the terminal S and furthermore the electromagnet M may be actuated by the exposure time control circuit J with the movable contact piece S engaging the terminal S whereby various types of exposure control may be effected. In this case, it is to be noted that the couplings 3A and 3D should be connected to each other and the contact pieces 1A and 2A should be connected to the contact pieces 18 and 28' respectively.

It should be understood that the present invention is not limited to the embodiments described herein, and that additional modifications and improvements are readily apparent to those skilled in the art within the scope and purview of the invention as defined by the claims that follow. Furthermore, it should be understood that the camera body need not necessarily be provided with the exposure time control circuit G, nor need the type of the exposure time control be limited to such exposure time control circuits as shown at G, H, H and J.

We claim:

1. An electrical exposure time control device for use I means for separably coupling the connecting terminals of said accessory to the connecting terminals of said camera body.

2. An electrical exposure time control device for use in a photographic camera as set forth in claim 1, wherein said camera further comprises:

an exposure time control circuit and switch means for interrupting the actuation of the electromagnet by said exposure time control circuit.

3. An electrical exposure time control device for use in a photographic camera as set forth in claim 2, wherein said-switch means is normally closed to actuate said exposure time control circuit, and means responsive to the coupling of said accessory terminals to said camera body terminals'for opening saidswitch means.

4. An electrical exposure time control device as set forth in claim 2, wherein one of the exposure time control circuits includes a light receiving element exposable to the light from the entire scene to be photographed and the other exposure time control circuit includes a light receiving element exposable to the light from a'specific limited area in the scene to be photographed.

5. An electrical exposure time control device as set forth in claim 1, wherein said camera body is a single lens reflex camera body provided with a focussing screen and said accessory is provided with a pentagonal prism removably mountedon said focussing screen.

6. An electrical exposure time control device as set forth in claim 5, wherein said single lens reflex camera comprises an exposure time control circuit and switch means for interrupting the actuation of said electromagnet by means of said exposure timecontrol circuit; one of said exposure time control circuits includes a light receivingelement which is exposable to light not traversing the objective lens mounted on said camera body, the other exposure time control circuit includes a light receiving element exposable to light traversing said objective lens and storage means for storing a voltage responsive to the light incident on said respective light receiving element, a timing circuit adapted to produce an output in response to the stored voltage in said storage means, a switching circuit responsive to the output from said timing circuit, and electrical couplings connecting said output to said electromagnet terminals.

7. An electrical exposure time control device as set forth in claim 6, wherein said pair of connecting terminals connected to the opposite terminals of said electromagnet consist of a pair of contact pieces; and wherein said connecting terminals, connected to the output terminalsof said switching circuit in said accessory provided with a pentagonal prism, have contact pieces engaging said pair of contact pieces, when said housing is mounted on said focussing screen of said camera body; whereby said switch means may interrupt the actuation of said electromagnet by the exposure time control circuit incorporated in said camera body.

8. An electrical exposure time control device for use in a photographic camera, comprising:

a camera body provided with at least a shutter, an

electromagnet operable to control the closing of said shutter and pairs of connecting terminals connected to the respective opposite ends of said electromagnet;

10 a plurality of accessories mountable on said camera body and having an exposure time control circuit for electrically controlling the exposure time and a pair of terminals connected to the output thereof; and

means for selectively connecting the connecting terminals of said camera body to the connecting terminals of the exposure time control circuit incorporated in a selected one of said plurality of accessories mounted on said camera body.

9. An electrical exposure time control device as set forth in claim 8, including an exposure time control circuit in said camera body and wherein said selectively connecting means includes normally closed switch means for actuating said exposure time control circuit incorporated in said camera body, and including means for opening said switch means in response to the connecting terminals of at least one of said plurality of accessories being connected to a pair of opposite terminals of said electromagnet.

10. An electrical exposure time control device as set forth in claim 8, wherein said camera body is a single lens reflex camera body provided with a focussing screen and wherein one of said plurality of accessories includes a housing provided with a pentagonal prism and is removably mounted on said focussing screen.

11. An electrical exposure time control device as set forth in claim 10, wherein said plurality of accessories are provided with a pentagonal prism and'include:

a first accessory comprising a housing enclosing a' first exposure time control circuit and a first coupling member with connecting terminals; a second accessory comprising a second exposure time control circuit and a second coupling member with connecting terminals, one of said first and second exposure time control circuits and the third exposure time control circuit incorporated in said camera body having a light receiving element positioned to receive the light from the entire scene to be photographed not traversing the camera objective lens mounted on said camera body, another circuit being provided with a light receiving element disposed to receive light from a specific area in the object scene, and a further circuit being provided with a light receiving element positioned to receive the light traversing the objective lens from the scene, storage means for storing a voltage responsive to the light incident on said light receiving element of said further circuit, a timing circuit responsive to said stored voltage, and a switching circuit responsive to said timing circuit.

12. An electrical exposure time control device as set forth in claim 10, wherein at least one pair of a plurality of connecting terminals which are connected to the opposite ends of said electromagnet consist of a pair of contact pieces and wherein the first connecting terminals, which are connected to the output terminals of a first accessory exposure time control circuit consist of a pair of contact pieces separably engageable with a pair of contact pieces of said electromagnet, said selective connecting means including switch menas for interrupting the actuation of the electromagnet by the exposure time control circuit incorporated in said camera body, when said both pairs of contacting pieces are connected to each other. 

1. An electrical exposure time control device for use in a photographic camera, comprising: a camera body including a shutter, an electromagnet controlling the closing of said shutter and a pair of connecting terminals connected to the terminals of said electromagnet; an accessory separably mounted to said camera body and including an electrical exposure time control circuit and a pair of connecting terminals engagable with the output of said exposure time control circuit; and means for separably coupling the connecting terminals of said accessory to the connecting terminals of said camera body.
 2. An electrical exposure time control device for use in a photographic camera as set forth in claim 1, wherein said camera further comprises: an exposure time control circuit and switch means for interrupting the actuation of the electromagnet by said exposure time control circuit.
 3. An electrical exposure time control device for use in a photographic camera as set forth in claim 2, wherein said switch means is normally closed to actuate said exposure time control circuit, and means responsive to the coupling of said accessory terminals to said camera body terminals for opening said switch means.
 4. An electrical exposure time control device as set forth in claim 2, wherein one of the exposure time control circuits includes a light receiving element exposable to the light from the entire scene to be photographed and the other exposure time control circuit includes a light receiving element exposable to the light from a specific limited area in the scene to be photographed.
 5. An electrical exposure time control device as set forth in claim 1, wherein said camera body is a single lens reflex camera body provided with a focussing screen and said accessory is provided with a pentagonal prism removably mounted on said focussing screen.
 6. An electrical exposure time control device as set forth in claim 5, wherein said single lens reflex camera comprises an exposure time control circuit and switch means for interrupting the actuation of said electromagnet by means of said exposure time control circuit; one of said exposure time control circuits includes a light receiving element which is exposable to light not traversing the objective lens mounted on said camera body, the other exposure time control circuit includes a light receiving element exposable to light traversing said objective lens and storage means for storing a voltage responsive to the light incident on said respective light receiving element, a timing circuit adapted to produce an output in response to the stored voltage in said storage means, a switching circuit responsive to the output from said timing circuit, and electrical couplings connecting said output to said electromagnet terminals.
 7. An electrical exposure time control device as set forth in claim 6, wherein said pair of connecting terminals connected to the opposite terminals of said electromagnet consist of a pair of contact pieces; and wherein said connecting terminals, connected to the output terminals of said switching circuit in said accessory provided with a pentaGonal prism, have contact pieces engaging said pair of contact pieces, when said housing is mounted on said focussing screen of said camera body; whereby said switch means may interrupt the actuation of said electromagnet by the exposure time control circuit incorporated in said camera body.
 8. An electrical exposure time control device for use in a photographic camera, comprising: a camera body provided with at least a shutter, an electromagnet operable to control the closing of said shutter and pairs of connecting terminals connected to the respective opposite ends of said electromagnet; a plurality of accessories mountable on said camera body and having an exposure time control circuit for electrically controlling the exposure time and a pair of terminals connected to the output thereof; and means for selectively connecting the connecting terminals of said camera body to the connecting terminals of the exposure time control circuit incorporated in a selected one of said plurality of accessories mounted on said camera body.
 9. An electrical exposure time control device as set forth in claim 8, including an exposure time control circuit in said camera body and wherein said selectively connecting means includes normally closed switch means for actuating said exposure time control circuit incorporated in said camera body, and including means for opening said switch means in response to the connecting terminals of at least one of said plurality of accessories being connected to a pair of opposite terminals of said electromagnet.
 10. An electrical exposure time control device as set forth in claim 8, wherein said camera body is a single lens reflex camera body provided with a focussing screen and wherein one of said plurality of accessories includes a housing provided with a pentagonal prism and is removably mounted on said focussing screen.
 11. An electrical exposure time control device as set forth in claim 10, wherein said plurality of accessories are provided with a pentagonal prism and include: a first accessory comprising a housing enclosing a first exposure time control circuit and a first coupling member with connecting terminals; a second accessory comprising a second exposure time control circuit and a second coupling member with connecting terminals, one of said first and second exposure time control circuits and the third exposure time control circuit incorporated in said camera body having a light receiving element positioned to receive the light from the entire scene to be photographed not traversing the camera objective lens mounted on said camera body, another circuit being provided with a light receiving element disposed to receive light from a specific area in the object scene, and a further circuit being provided with a light receiving element positioned to receive the light traversing the objective lens from the scene, storage means for storing a voltage responsive to the light incident on said light receiving element of said further circuit, a timing circuit responsive to said stored voltage, and a switching circuit responsive to said timing circuit.
 12. An electrical exposure time control device as set forth in claim 10, wherein at least one pair of a plurality of connecting terminals which are connected to the opposite ends of said electromagnet consist of a pair of contact pieces and wherein the first connecting terminals, which are connected to the output terminals of a first accessory exposure time control circuit consist of a pair of contact pieces separably engageable with a pair of contact pieces of said electromagnet, said selective connecting means including switch menas for interrupting the actuation of the electromagnet by the exposure time control circuit incorporated in said camera body, when said both pairs of contacting pieces are connected to each other. 